This invention generally relates to a process for coating articles with a sprayed-on organic polymeric material in a powdered form. More particularly, this invention relates to such a process in which the articles are pre-heated before being coated. Specifically, this invention relates to such a process wherein the pre-heated articles are transferred to a cool conveying mechanism after being pre-heated to reduce the coating of the conveying mechanism with the material being sprayed on the article.
The technique of spraying organic polymeric material in a powdered form onto articles to thereby coat the articles is known in the art. Also known is pre-heating the article prior to spraying and heating the article after spraying to cure the material so applied. Glass containers in particular may be so coated to provide a fragment-retentive coating on the container in the event of breakage of the container. However, a recurring problem in so coating glass containers has been that of material build-up on chucks which carry the glass containers through the process. This results because the chucks become heated during the pre-heat procedure and any oversprayed material during the spray process melts on the hot chucks, thus tending to coat them. Within a rather short period of time, the chucks are so badly coated that their operation is impaired, and the process must be shut down for cleaning. We have found that glass containers may be preheated while being carried by one set of chucks and then transferred to a second set of cool chucks for transport through the spray apparatus. We can do this without losing alignment of the containers and without significant loss of pre-heat temperature. Any powder-sprayed material which does reach the cold chuck does not melt or adhere thereon, and may later be removed by any suitable means. This procedure significantly extends the time period between process shutdowns for cleaning purposes.